The present invention relates to sizing compositions and methods of sizing paper. The sizing compositions of this invention comprise at least one hydrophobic substance which is not a sizing agent, at least one sizing agent selected from ASA, AKD and rosin where the sizing agent is emulsified in water, and at least one emulsion stabilizer.
This invention relates to paper sizing, i.e., rendering paper more resistant to penetration by liquids, such as inks. The control of the penetration of liquids, such as aqueous inks, into paper and the water-resistance of paper are important properties of many grades of paper and for many applications. Control of ink penetration is important in writing and printing grades and, especially, for ink-jet printing. For example, good printing performance may require a limited amount of wetting by the ink but the rate of penetration of the ink into the sheet should be low.
Paper and paperboard are often sized with various sizing agents, such as alkyl and alkenyl succinic anhydride (hereafter xe2x80x9cASAxe2x80x9d), alkyl and alkylene ketene dimers (hereafter xe2x80x9cAKDxe2x80x9d), rosin and rosin derivatives such as rosin soap, starch, sodium silicate, fluorocarbons, certain styrene-maleic anhydride copolymers and cyclic dicarboxylic acid anhydrides. Sizing can be accomplished by either internal sizing processes, which usually involve wet end addition, or surface sizing processes, which usually involve addition at the size press. For effective sizing of paper pulp, it is desirable that the sizing agent be uniformly distributed throughout the fibrous slurry of pulp. Therefore, sizing agents may be emulsified to a small particle size using an emulsion stabilizer and the aqueous sizing emulsion is then added to the pulp at the wet end of the papermaking process. Emulsion stabilizers commonly used to prepare sizing emulsions include, for example, cationic starches and cationic polymers.
Certain sizing agents, such as ASA and AKD which are reactive substances capable of forming chemical bonds to the paper surface, also tend to be reactive with water. Therefore, sizing emulsions comprising such materials may be prepared at a paper mill and added immediately to the wet end of the paper making process in order to minimize reactions between water and the sizing agent.
Aqueous emulsions comprising ASA as the sizing agent are described in U.S. Pat. No. 3,102,064 to Wurzburg et al. (hereafter xe2x80x9cthe ""064 patentxe2x80x9d). The ASA sizing emulsions disclosed in the ""064 patent must additionally comprise either a cationic agent or an agent that is capable of disassociating to yield one or more cations. Cationic agents disclosed in the ""064 patent are various cationic starch derivatives which can be prepared from a variety of starches including corn, tapioca and potato. However, these ASA sizing emulsions can cause various problems when used in making paper, including machine deposits and continuity problems in the form of press picking, felt filling, and poor cylinder vat consistency control.
U.S. Pat. No. 4,657,946 to Rende et al. (hereafter xe2x80x9cthe ""946 patentxe2x80x9d) discloses aqueous ASA emulsions said to be improved over those of the ""064 patent. The ""946 patent discloses cationic water soluble vinyl addition polymers with molecular weights greater than about 10,000 and preferably below about 1,000,000 as emulsifiers or co-emulsifiers for ASA sizing emulsions. However, the sizing emulsions of the ""946 patent suffer from a short shelf life and are prepared by mixing with an expensive high shear mixer.
U.S. Pat. Nos. 4,711,671 and 4,747,910 (hereafter xe2x80x9cthe ""671 patentxe2x80x9d and xe2x80x9cthe ""910 patentxe2x80x9d, respectively) disclose shelf storable, self-emulsifying paper sizing reagents containing highly ethoxylated lanolin, i.e., at least about 15 moles of ethylene oxide per mole of lanolin. Each of these two patents discloses compositions containing between about 1 and 20 parts by weight ethoxylated lanolin with a composition containing about 1% ethoxylated lanolin showing the greatest improvement in storage stability. However, the disclosure in these references provide, at most, minimal sizing improvements (less than about a 9.5% increase in HST size after 1 month accelerated aging) over the control ASA emulsion.
U.S. Pat. Nos. 4,728,366 and 4,832,792 disclose shelf storable, self-emulsifying paper sizing reagents containing highly ethoxylated castor oil, i.e., at least about 5 moles of ethylene oxide per mole of castor oil. Each of these two patents discloses compositions containing between about 1 and 15 parts by weight ethoxylated castor oil with a composition containing about 7% ethoxylated castor oil showing the greatest improvement in storage stability but with a minimal (about a 21% increase in HST size) sizing improvement over the control ASA emulsion.
Therefore, a need remains in the art for sizing compositions having improved emulsion quality, e.g., with median particle sizes of less than about 5 xcexcm and preferably less than about 3 xcexcm, sizing performance and operability, particularly with respect to conventional sizing emulsions such as those containing ASA or AKD. The present invention provides such improved sizing emulsions. Moreover, since typical sizing agents such as ASA and AKD tend to have very low solubility in water, there remains a problem in that the sizing efficiency of the sizing agent is less than is desired because the sizing agent is not uniformly distributed throughout the paper in a manner that gives maximum sizing. Additionally, because a large percentage of a conventional sizing agent is not always retained by the paper, operability problems and economic disadvantages arise when the nonretained conventional sizing agent goes instead into the white water. Surprisingly, the instant inventors have discovered that the sizing efficiency of a sizing agent is increased when it is contained in a sizing composition that also contains a hydrophobic substance that is not a sizing agent. The teachings of all patents and other literature articles referenced herein are incorporated herein by reference.
One embodiment of the present invention relates to a paper sizing composition comprised of at least one sizing agent selected from ASA, AKD and rosin where the sizing agent is emulsified in water, at least one emulsion stabilizer, and from about 0.01% to about 15% by weight of at least one hydrophobic substance, based on the total weight of sizing agent present, where the hydrophobic substance is not highly alkoxylated. The sizing promotion efficiency of this paper sizing composition as determined by at least one method selected from the Cytec size testing method, the Hercules size testing method, and the Cobb size testing method is greater than or equal to about 4. Preferably, the quantity of hydrophobic substance present is from about 0.1% to about 10% by weight based on the total weight of sizing agent present. Preferably, the sizing promotion efficiency of the paper sizing composition is greater than or equal to about 6 and, more preferably, greater than or equal to about 10.
The hydrophobic substance may be selected from the group consisting of fatty acid esters, triglycerides, hydrocarbons, esters derived from ASA, amides derived from ASA, silicone oils, alcohols, and mixtures thereof and the sizing agent may be at least one synthetic sizing agent. Preferably, the sizing agent is selected from ASA, AKD, and mixtures thereof. More preferably, each sizing agent, independently, has an alkyl or alkenyl group comprising from about 8 to about 36 carbon atoms. Alternately, the sizing agent is at least one succinic anhydride substituted, independently, by a substantially linear alkyl or alkenyl group comprising from about 16 to about 18 carbon atoms. The quantity of sizing agent present is from about 3% to about 38% by weight based on the total weight of emulsion present.
A suitable emulsion stabilizer may be selected from cationic synthetic polymers, cationic starches, and mixtures thereof. The quantity of emulsion stabilizer present in the paper sizing composition may be from about 9% to about 400% by weight based on the total weight of sizing agent present. Preferably, the emulsion has a median emulsion particle size of about 5 xcexcm or less and, more preferably, about 3 xcexcm or less.
Another embodiment of the present invention relates to a paper sizing composition comprised of at least one sizing agent selected from ASA, AKD and rosin where the sizing agent is emulsified in water, at least one emulsion stabilizer, and from about 0.01% to about 15% by weight of at least one hydrophobic substance, based on the total weight of sizing agent present, where the sizing promotion efficiency of the paper sizing composition as determined by at least one method selected from the Cytec size testing method, the Hercules size testing method, and the Cobb size testing method is greater than or equal to about 4. The hydrophobic substance is selected from the group consisting of fatty acid esters comprising aliphatic fatty acid portions containing from about 7 to about 41 carbon atoms, which are optionally monounsaturated or diunsaturated and, whether unsaturated or not, are optionally substituted with at least one hydroxy group, triglycerides comprising aliphatic fatty acid portions containing from about 4 to about 22 carbon atoms, which are optionally monounsaturated or diunsaturated and, whether unsaturated or not, are optionally substituted with at least one hydroxy group, substantially straight chain hydrocarbons containing from about 6 to about 34 carbon atoms, which are optionally terminally unsaturated and, if unsaturated, are optionally isomerized, ASA derivatives formed from the reaction products of about 1 mole of ASA with about 1 mole of 1-octadecanol or 1-hexadecylamine, about 0.2 moles cholesterol or about 1 mole cholesterol, and the reaction products of about 9.25 or of about 3 moles ASA with about 1 mole castor oil, the silicone oils poly(dimethylsiloxane) optionally comprising side chains selected from PEO, PPO, and mixtures thereof, poly(diphenylsiloxane), poly(methylphenylsiloxane), poly(t-butyl-methylsiloxane), poly(dimethylsiloxane-co-alkylmethylsiloxane) where the alkyl comprises, independently, from about 1 to about 18 carbon atoms, poly[dimethylsiloxane-co-3-(aminopropylmethylsiloxane)], hydride- terminated poly(dimethylsiloxane), and distearate-terminated poly(dimethylsiloxane), aloe-emodin, aloin, cholesterol, lanosterol, and mixtures thereof, provided that the hydrophobic substance is not highly alkoxylated.
A further embodiment of the invention relates to a paper sizing composition comprised of at least one sizing agent selected from ASA, AKD and rosin where the sizing agent is emulsified in water, at least one emulsion stabilizer, and from about 0.01% to about 15% by weight of lanolin, based on the total weight of sizing agent present, with the proviso that the lanolin is not highly alkoxylated, where the sizing promotion efficiency of the paper sizing composition as determined by at least one method selected from the Cytec size testing method, the Hercules size testing method, and the Cobb size testing method is greater than or equal to about 10. The sizing agent in this composition is selected from ASA, AKD, and mixtures thereof where each sizing agent, independently, has an alkyl or alkenyl group comprising from about 8 to about 36 carbon atoms. Preferably, the sizing agent is at least one succinic anhydride substituted, independently, by a substantially linear alkyl or alkenyl group comprising from about 16 to about 18 carbon atoms. Each emulsion stabilizer present may be suitably selected from cationic synthetic polymers, cationic starches, and mixtures thereof. The quantity of all emulsion stabilizers present may be from about 9% to about 400% by weight based on the total weight of sizing agent(s) present.
An additional embodiment of the invention relates to a method for sizing paper products, the method comprising forming a paper sizing composition, such as any of those described above, dispersing the composition throughout a paper stock, and optionally forming a web from the paper stock on a paper making machine to form a sized paper product. The method may also include passing the sized paper product through a drying stage.
An alternate embodiment of the present invention relates to paper or paperboard treated with any sizing composition described above.